The proposed research involves studies of the specific role water plays in protein structure and function. Several new experimental approaches are presented: 1. Studies of the thermodynamics of the interaction of strongly held water with proteins by sorption isotherm measurements. 2. Studies of protein conformational changes which occur upon removal of water by means of sorption isotherm reversibility measurements and difference hydrogen exchange measurements. 3. Studies of protein functional changes which occur upon removal of water by studies of oxygen and carbon monoxide binding by myoglobin and hemoglobin as a function of water removal.